Almanac & sky · NUMORA
Moon Phase Calculator
You want the four pillars straight: when the year flips, which two-hour branch, and whether longitude is corrected.
Open interactive calculatorHow to use
Abbreviated lunar theory — not Swiss Ephemeris.
Formula
elongation ≈ |λ☾ − λ☉|; illum = (1 − cos i) / 2
FAQ
Is this Moon Phase calculator accurate?
The formula and assumptions are shown on the page, and the engine is covered by audit tests. Results are for reference — not financial or medical advice.
Do I need an account?
No. Calculations run in your browser. Recents can stay on this device.
What inputs do I need?
Abbreviated lunar theory — not Swiss Ephemeris.
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